Various construction methods have been suggested for underground construction by excavating the ground. As such construction methods, following methods are known. One example construction method includes installing a diaphragm wall for temporary installation in the ground, excavating a surface side thereof, and thereafter constructing a main body wall for main installation. Another example construction method includes constructing a soil cement wall or a cast-in-place reinforced concrete wall, which can be used for both temporary installation and main installation, in the ground.
However, among such construction methods in which the diaphragm wall for temporary installation is used, in a construction method in which a concrete-based wall body such as a soil cement wall or a cast-in-place reinforced concrete wall is used as a diaphragm wall for temporary installation, there is a problem in that the diaphragm wall for temporary installation cannot be removed after constructing the underground structure, and may cause issues when a new underground structure is constructed in the vicinity of the diaphragm wall for temporary installation, which was installed in advance.
In addition, as a construction method in which a steel-based wall body which can be pulled out and removed is used as the diaphragm wall for temporary installation, a soldier piles and lagging construction method and a steel sheet pile construction method are known. However, in these construction methods, in the cases where the depth of excavation is greater than about 10 m, there are problems in that in many cases the steel-based wall body has insufficient cross-sectional stiffness and is not easily applied, and in that ancillary structures such as a tie rod or an anchor are needed.
In order to deal with the above problems, as an earth-retaining member, which is a steel for the diaphragm wall having excellent cross-sectional stiffness and has a large cross-section to be applied to a construction in which the depth of excavation is about 10 m or greater, a steel pipe sheet pile in which a steel pipe with a slit having a diameter of about 165 mm is attached to a steel pipe of about 500 to 2000 mm as a joint has been used.
In addition, as another wall material having excellent cross-sectional stiffness to be used in the diaphragm wall, a combined steel sheet pile having a combination of a steel sheet pile and an H-shaped steel has been used. For example, a combined steel sheet pile in which a steel sheet pile and an H-shaped steel are joined together by continuous or intermittent welding is known.
For example, Patent Document 1 discloses a combined steel sheet pile in which an H-shaped steel is joined by welding to a linear steel sheet pile having left and right joints that are asymmetric in shape.
In addition, Patent Document 2 discloses, as illustrated in FIGS. 29A and 29B, a combined steel sheet pile 101 in which an H-shaped steel 130 is joined to a steel sheet pile 110 which has a hat-shaped cross-section and has left and right joints 111 that are asymmetric in shape. In order to join the H-shaped steel 130 to the steel sheet pile 110, the combined steel sheet pile 101 uses welds W as illustrated in FIG. 29A or uses joining bolts 141 and joining nuts 145 as illustrated in FIG. 29B.
In addition, Patent Document 3 discloses a combined steel sheet pile in which a processing tool is provided to one surface of front and rear surfaces of a steel sheet pile to cause a section steel such as an H-shaped steel to be fitted as a stiffener.
In addition, Patent Document 4 discloses a combined steel sheet pile formed of a steel sheet pile having a web at a center portion in the width direction and joints at both ends, and an H-shaped steel having flanges at the ends of a web, in which the web of the steel sheet pile and one flange of the H-shaped steel overlap each other and are joined together by a drill screw to protrude from the flange of the H-shaped steel.